Ferdinando Pizzo

Recent Advances in Lewis Acid Catalyzed Diels−Alder Reactions in Aqueous Media

Recently the aqueous medium has attracted the interest of organic chemists, and many, sometimes surprising, discoveries have been made. Among the organic reactions investigated in aqueous medium, the Diels−Alder cycloaddition has been the most widely studied because of its great importance in the synthetic and theoretical fields. The Diels−Alder reaction is greatly enhanced by Lewis acid catalysis, and this review illustrates recent significant results in this field when the reaction is performed in aqueous medium.

Condensation reactions in water of active methylene compounds with arylaldehydes. One-pot synthesis of flavonols

Abstract The condensation reactions of acetophenone, cyclohexanone, isophorone, phenylacetonitrile, p-nitrophenylacetonitrile, (phenylsulfonyl)acetonitrile and indene with benzaldehyde were studied in water in heterogeneous phase in the presence and absence of anionic and cationic surfactants such as SLS, CTACl, (CTA)2SO4 and CTAOH. All the reactions occur with excellent yields. The cationic surfactants favour the reaction and the comparison with the corresponding tetrabutylammonium salts show that the micellar catalysis is effective mainly towards the dehydration reaction following that of condensation. Anionic surfactant SLS is inactive. 2′-hydroxychalcones were prepared in aqueous medium in good-excellent yields and the one-pot synthesis of 7- and 3′,4′-substituted flavonols was achieved.

Recent developments on the chemistry of aliphatic nitro compounds under aqueous medium

Aliphatic nitro derivatives represent an important class of useful molecules in organic synthesis. The versatility of these compounds is largely due to their easy availability and transformation into a variety of diverse functionalities. Moreover, aliphatic nitro compounds are very important building blocks (both as nucleophiles or as electrophiles) for the generation of new carbon–carbon bonds, mainly via nitroaldol-Henry reactions, Michael reactions and Diels–Alder cycloadditions. Usually, organic solvents are believed to be necessary for achieving the best efficiency in the reactions of aliphatic nitro compounds and, only recently, it has been shown that these reactions are also very efficient using water as reaction medium. Such progress in the chemistry of aliphatic nitro compounds is particularly attractive to industry since the replacement of toxic solvents still remains a crucial (and expensive) challenge. Thus, this report is focused on the chemistry of aliphatic nitro derivatives performed in aqueous media.

Thiolysis of 1,2-epoxides by thiophenol catalyzed under solvent-free conditions

Thiolysis of alkyl- and aryl-1,2-epoxides was investigated under solvent-free conditions in the presence of Lewis and Bronsted acid and base catalysts (InCl3, p-TsOH, n-Bu3P, K2CO3). Five mol% of catalyst was sufficient and the best results were obtained by using InCl3 and K2CO3. β-Hydroxy sulfide was isolated in excellent yields.

γ-Valerolactone as an alternative biomass-derived medium for the Sonogashira reaction

γ-Valerolactone (GVL) can be used as an efficient and practical alternative to the banned and commonly used dipolar aprotic solvents. In this contribution GVL has been used as a non-toxic, biodegradable, biomass-derived medium, for the definition of a simple and general protocol for the Sonogashira cross-coupling reaction. The chemical efficiency of GVL as a medium is excellent and the best results have been obtained using DABCO as the base allowing the isolation of products 3a–q in 60–96% yields. These results represent an example which proves that biomass-derived safer solvents can be used efficiently in common transformations reaching higher greenness/sustainability as well as high chemical efficiency.

Sc(III)-Catalyzed Enantioselective Addition of Thiols to α,β-Unsaturated Ketones in Neutral Water

This report concerns Lewis acid catalyzed enantioselective sulfa-Michael addition in neutral water by using a very efficient Sc(OTf)(3)/bipyridine 1 catalytic system. It is noteworthy that the protocol presented employs water as a reaction medium and allows us to obtain very high stereoselectivity and satisfactory yields for β-keto sulphides deriving from aliphatic thiols. The recovery and reuse of both the aqueous medium and the catalytic system is also reported.

A green route to β-amino alcohols via the uncatalyzed aminolysis of 1,2-epoxides by alkyl- and arylamines

Under mildly basic and pH-controlled aqueous conditions the aminolysis of 1,2-epoxides 1a–g by alkyl- and arylamines 2a–k is generally highly regioselective giving the corresponding β-amino alcohols in satisfactory to excellent yields.

Epoxidation of α,β-unsaturated ketones in water. An environmentally benign protocol

An easy, cheap procedure is proposed for the epoxidation of α,β-unsaturated ketones in water as the sole reaction medium and using bases such as NaOH and CTAOH as promoting agents and hydrogen peroxide as oxidant. By using solely water, the reaction medium can be recycled which is important for reducing wastes. An example of an α-functionalization of α,β-unsaturated ketones by a one-pot procedure in water is reported.

Water, a clean, inexpensive, and re-usable reaction medium. One-pot synthesis of (E)-2-aryl-1-cyano-1-nitroethenes

The Knoevenagel addition of aryl aldehydes 1 with nitroacetonitrile 2 in water followed by dehydration of β-nitroalcohols 3, allows (E)-2-aryl-1-cyano-1-nitroethenes 4 to be prepared by a one-pot procedure without using organic solvents. The reuse of the aqueous medium makes this process inexpensive and highly environmentally friendly. The protocol was used to synthesize the benzo[b]pyrane [4,3-d][1,2]oxazine-2-oxide skeleton by a domino Knoevenagel–Diels–Alder process.

Epoxidation reaction with m-chloroperoxybenzoic acid in water

Abstract Epoxidation reaction of liquid alkenes with m-chloroperoxybenzoic acid in water at room temperature gives oxiranes in high yield.